1. Field of the Invention
The present invention relates to improvements in polishing discs and the method of making them, and in particular to a polishing disc cut from sheet abrasive material and adhered to an inexpensively produced plastic hub that locks onto a rotatable arbor.
2. Description of the Prior Art
In the field of dentistry it is necessary to contour, finish and polish restorative dental materials once they have been placed into or onto a tooth so that the restorative materials blend to the contour of the tooth with a smooth transition between the material and tooth structure. It is imperative that the restorative materials be highly polished to prevent plaque build up which leads to other complications.
The most common dental restorative materials currently used are composite, amalgam, gold, ceramics, acrylic, and glassionomers. These as well as other polishable materials usually require polishing with a minimum of at least two steps of sequential grits, with most materials requiring three to six steps before achieving satisfactory results. This series of polishings usually requires single-use, disposable discs having a sequence of grit sizes. For this reason, not only must dental polishing discs be inexpensive in terms of material and manufacturability, but to save dentists' time they must also be capable of being very quickly secured to and removed from a driving arbor. Because the dental polishing discs is used inside a patient's mouth, it must be relatively small, and be rigidly secured to the arbor so it won't wobble or fly off.
Several prior art devices are available for this purpose. Generally they are comprised of grit coated thin discs of paper or plastic or thin rigid discs of abrasive, having a central aperture to receive a screw, pin, shaft or the like, by means of which the disc can be secured to a rotary drive shaft or arbor. With most prior art, the head of the shaft or arbor protrudes from the forward face of the dental polishing disc and clamps to the inner area of the disc by means of a metal or plastic eyelet that may be swaged through the disc. The protrusion of the shaft or arbor beyond the dental polishing disc limits the working area of the disc, and during polishing can inadvertently cause damage to the restorative material, tooth structure, or tissue.
U.S. Pats. Nos. 3,858,368 and 4,447,208 disclose a dental polishing disc in which the central hub or the entire polishing head is made of soft rubber. The central hub of such dental polishing discs are formed with a blind, hollow, cylindrically-shaped interior cavity having at least one flattened surface so a head portion of the arbor may be inserted into the cavity thus securing the disc to the arbor. The central hubs of these molded dental polishing discs can either be molded integrally with the polishing disc or molded separately and attached to the disc by means of an adhesive material. Because these dental polishing discs have a blind interior cavity the arbor cannot protrude beyond the dental polishing disc. Thus, dental polishing discs having molded rubber hubs prevent inadvertently damaging restorative material, tooth structure, or tissue. However, the molded central hub or entire polishing head is comparatively expensive, bulky, and can be manufactured only in a limited range of shapes and sizes. Using a blind hole configuration as in these devices, there always exists a rubber filled space between the disc and the arbor which remains flexible thus permitting the dental polishing disc to wobble on the arbor. Furthermore, due to poor engagement between the molded rubber hub and the arbor such dental polishing discs tend to fly off the arbor when polishing with the surface of the disc adjacent to the arbor.